public class Zuoye4{

	public static void main(String[] args){
		int sum = 0;
		int a = 0;
		/*for(int i = 0;i <= 100;i++){
		
			if(i % 2 == 0){
			
				sum = sum + i;
			}else{
			
			sum = sum - i;
			}
		}
		a = sum + 1;
		System.out.println(a);*/
		int i = 0;
		while(i <= 100){
			if(i % 2 == 0){
			
				sum = sum + i;
			}else{
			
			sum = sum - i;
			}
			i++;
			continue;
			
			
		}
		a = sum + 1;
		System.out.println(a);
	}

}